1. Field of the Invention
This invention relates to a drive unit structure for keyboard assemblies, and more particularly to a drive unit structure for a keyboard assembly, which is comprised of a driving member and a driven member.
2. Prior Art
A conventional keyboard assembly for use in electronic keyboard musical instruments in general is provided with various drive units formed of driving members (actuators) and driven members driven by the driving members or actuators. For example, a drive unit structure for a keyboard assembly of this kind is generally known, which is comprised of a mass member associated with a key, for imparting inertia to an operation of depressing the key, a key switch driven by the mass member, for detecting the key depressing operation. The mass member is pivotally moved in response to the key depressing operation, and the key switch is driven through the pivotal movement of the mass member.
In the above driver mechanism, the key and the mass member forms a drive unit, wherein the key is an actuator and the mass member is a driven member, and the mass member and the key switch also form a drive unit, wherein the mass member is an actuator and the key switch is a driven member.
These drive units are generally constructed such that the actuator and the driven member (or the driven member alone) are each pivotally moved about a fulcrum thereof, and when the actuator is pivotally moved, a portion of the actuator contacts the driven member to cause pivotal movement of the same. Usually, at least one of the actuator and the driven member has a flat surface portion thereof adapted for contact with the other. More specifically, for example, a tip or free end portion of the actuator is shaped in the form of a curved surface, while a corresponding portion of the driven member is shaped in the form of a flat surface, and the curved surface of the actuator contacts the flat surface of the driven member so that the driven member is driven by the actuator.
In the conventional drive unit structure, however, the influence of friction between the actuator and the driven member occurring during driving operation of the actuator is not fully contemplated, and therefore, the conventional drive unit structure remains to be improved in stableness of driving operation.
More specifically, in the conventional drive unit structure, the axes of the fulcrum shafts of the actuator and the driven member are not in alignment with each other. Therefore, when the driven member is pivotally moved through the pivotal movement of the actuator, the two members necessarily slide against each other. Since the actuator thus drives the driven member while the former is in sliding contact with the latter, a frictional force is generated between the two members.
FIG. 1 shows an example of the conventional drive unit structure. In FIG. 1, reference numeral 101 designates an actuator which forms part of a key, for example. The actuator 101 has a convex protuberance 101a at its tip and is movable in vertical directions as viewed in the figure. Reference numeral 102 designates a driven member which is a mass member or a key switch. The driven member 102 has a flat sliding surface 102a and is pivotable about a fulcrum shaft thereof.
The protuberance 101a of the actuator 101 drives the driven member 102 in such a manner that the protuberance 101a slidingly urges the sliding surface 102a of the driven member 102. During this driving operation, the actuator 101 moves downward almost straight, and accordingly sliding occurs between the protuberance 101a and the sliding surface 102a in leftward and rightward directions as viewed in the figure so that a frictional force F is generated. The frictional force F acts upon the sliding surface 102a in the sliding direction, and therefore the moment of rotation M about the fulcrum shaft 103 is expressed as M=F.times.L, where L represents the minimum distance between the axis of the fulcrum shaft 103 and a plane including the sliding surface 102a, which changes with the driving stroke of the actuator 101. In the illustrated example, the frictional force F acts upon the actuator 101 and the driven member 102, and the moment of rotation M acts upon the driven member 102. In an arrangement that the actuator 101 is pivotable about a fulcrum shaft thereof, the actuator 101 is also acted upon by the moment of rotation.
If the driven member is a mass member having large inertia or a switch whose switching operation directly affects the key depression accuracy, the frictional force F between the actuator and the driven member is so large that it cannot be ignored. Particularly, in the case where the actuator and the driven member are both rotatable members, the frictional force acts upon the actuator and the driven member as the moment of rotation, and appreciably affects the operation of the drive unit if it is large in magnitude.
Further, at a time point of acceleration of the key such as an initial stage of depression of the key and an initial stage of return of the key from a lower limit position or at the termination of key depression stroke (so-called key flapping position at the end of key depression stroke), a particularly smooth and quick motion is required of the drive unit. Besides, a sensitive driving motion as intended is required of the drive unit for accurate detection of depression of the key. A large frictional force, however, badly affects the operation of the drive unit.
More specifically, in the conventional drive unit structure, the frictional force generated between the actuator and the driven member can make the operations of the actuator and the driven member unstable so that the operation of the actuator cannot be properly transmitted to the driven member. For example, if the drive unit performs key depressing operation, the key depression resistance increases, resulting in a degraded feeling of touch and degraded accuracy of detection of key depression.
The conventional electronic keyboard musical instruments provided with drive units formed of keys and key switches include a type which electrically reproduces sounds of acoustic musical instruments such as grand piano and pipe organ in response to key depressions detected by the key switches. The electronic keyboard musical instruments of this type include those which are adapted to have a key depression feeling close to that of a natural musical instrument. For example, a keyboard musical instrument is known which uses mass members to impart appropriate inertia to the key depressing operation to thereby obtain a key depression feeling close to that of a grand piano.
FIG. 2 is a graph showing key depression resistance obtained by the known keyboard musical instrument provided with a drive unit structure using mass members. In the figure, the ordinate represents a key position ST during key depression stroke, and the abscissa represents a load transmitted to the finger through the key (key depression resistance FK"). Symbol STO" on the abscissa indicates a key depression starting position (upper limit position or non-depressed position of the key), ST1" a position of the key (or the actuator, not shown) in which the key contacts the switch, and STF" a lower limit position of the key (after execution of the full stroke). In this electronic keyboard musical instrument, by virtue of a mass member, between key positions STO" and ST1', the key depression resistance FK" exhibits a close characteristic to that of a grand piano in general, particularly in the depressing stroke, thus obtaining a key depression feeling which is close to that of a genuine or natural grand piano to some degree.
It is, however, difficult to perfectly reproduce a key depression feeling of a genuine acoustic musical instrument. For example, in the case of a grand piano, the key depression resistance generally slowly progressively increases during key depression stroke and sharply rises near the lower limit position at the completion of the key depression, while intricately varying due to pivoting of a jack, a frictional force generated between the jack and its associated roller pad. The characteristic of change of the key depression resistance differs depending upon the kind of the musical instrument. It is not realistic to provide the electronic keyboard musical instrument with a key depressing mechanism similar or identical to that of a natural musical instrument to reproduce a key depression feeling of the same.
The key switches used in electronic keyboard musical instruments in general are formed of a resilient material such as rubber, and characteristics of the resilient material affects the key depression resistance.
FIGS. 3A and 3B are sectional fragmentary views showing a drive unit structure of a conventional keyboard assembly provided with key switches formed of a resilient material as mentioned above. FIG. 3A shows the drive unit structure at an initial stage of key depression stroke, and FIG. 3B shows the same at termination of the key depression stroke.
A switch 203 which is a driven member is formed of Ian elastic material such as a resilient resin, and has a swelled portion 203a which is pivotably supported on a fulcrum P3'. An actuator 202 which is a key driven through key depressing operation (or a member driven through a key) is pivotably supported on a fulcrum P2'. The actuator 202 is disposed in contact with the swelled portion 203a of the switch 203 at a point of contact Q' to urgingly drive the switch 203. The distance L1' between the fulcrum P2' and the point of contact Q' and the distance L2' between the fulcrum P3' and the point of contact Q' hardly vary during the time from the initial stage of key depression stroke (FIG. 3A) to the termination of the same (FIG. 3B).
When the switch 203 is driven, a skirt portion 203aa of the swelled portion 203a is deflected and hence the swelled portion 203a is buckled so that a pair of movable contacts SW' are brought into contact with respective fixed contacts FS', whereby a key depression is detected. On this occasion, a reaction force is generated in the swelled portion 203a as the swelled portion 203a is deflected. Since the distances L1' and L2' remain almost constant as mentioned above, the characteristic of change of the key depression resistance FK" depends upon the reaction force. Consequently, as shown in FIG. 2, the key depression resistance FK" once rises just after the key position ST1", drops just before the key position STF" as indicated by a circle Z, and sharply rises at the key position STF". That is, while the key depression resistance FK" is low, the key strikes on a lower stopper, not shown, for limiting a lower limit position at the end of key depression stroke, whereupon a vibration caused by the striking is transmitted to the finger through the drive unit. A feeling of touch based upon such a key depression resistance characteristic is different from a good feeling of touch inherent in a grand piano (a feeling that the key sticks to its lower limit position), and a player will have a degraded feeling of after touch in particular.
Thus, in electronic keyboard musical instruments, the key depression feeling, particularly the feeling of after touch depends upon characteristics of the material forming the switches such as buckling strength and reaction force, and therefore it is difficult to reproduce the real key depression feeling of an acoustic musical instrument. As noted above, in the illustrated drive unit formed of a key and a switch, the key depression feeling depends upon the key depression resistance during the characteristic of change of key depression stroke, i.e. key driving resistance that the key receives. Also in other drive units, it is desirable that the characteristic of change of the driving resistance can be freely set.